1. Field of the Invention
The present invention relates to a pixel structure and a display panel, and more particularly, to a pixel structure and a liquid crystal display panel suitable for an optically compensated birefringence liquid crystal display (OCB LCD).
2. Description of the Related Art
Since the demand of the display is increased gradually, the display vendors have dedicated themselves in developing new display techniques. Since the cathode ray tube (CRT) is advantageous in its better display quality and technology maturity, it has dominated the display market for a long time. However, since the concept of green environment is widely accepted recently, due to its characteristics of consuming more energy and generating more radiation, and little improvement in flattening its product, the CRT is not able to meet the market trend of being lighter, thinner, shorter, smaller, and having lower power consumption. Accordingly, the thin film transistor liquid crystal display (TFT-LCD) with superior characteristics of high picture quality, effectiveness of space utilization, low power consumption, no radiation, has gradually become the main stream in the display market.
Depending on various types of the liquid crystal, the driving methods, and the locations where the light source is disposed, the liquid crystal display can be classified as many different types. In particular, the optically compensated birefringence liquid crystal display (OCB LCD) has extremely fast response speed and is also capable of providing smooth pictures when the computer is playing the continuous pictures with fast changes such as the motion pictures or movies, thus it is suitable for applying in the high end liquid crystal display panel. However, the OCB LCD can enter into the standby mode for improving its fast response performance only when some liquid crystal molecules are transited from the splay state to the twist state and eventually transited to the bend state.
FIG. 1A is a schematic view of the liquid crystal molecules with the splay state in the liquid crystal display panel, and FIG. 1B is a schematic view of the liquid crystal molecules with the bend state in the liquid crystal display panel. Referring to FIGS. 1A and 1B, in the OCB LCD 10, a liquid crystal layer 11 is disposed between a top substrate 12 and a bottom substrate 13. The top substrate 12 and the bottom substrate 13 have their respective alignment layers (not shown) whose rubbing directions are parallel to each other. The liquid crystal molecules in the liquid crystal layer 11 are arranged with the splay state when there is no external electric field applied thereon. In case the OCB LCD desires entering into the standby mode, an electric field perpendicular to the top substrate 12 should be applied onto the liquid crystal molecules, such that some liquid crystal molecules can gradually transit to the twist state, and then transit to the bend state. In the conventional OCB LCD, this transition takes a couple of minutes to normally drive the pixels, in other words, a long time of warm up is required before the OCB LCD can enter into the standby mode. However, this problem is disadvantageous to the “ready-to-use” property of the liquid crystal display panel. Accordingly, a fast transition is required for the customers to easily accept the OCB LCD.
In order to have the liquid crystal molecules in the OCB LCD transit from the splay state to the bend state more quickly, a more intensive electric field is generated by increasing the voltage in the prior art, such that the liquid crystal molecules can quickly transit from the splay state to the bend state. However, since it is very hard to obtain the appropriate driving chip that is capable of enduring the high voltage, it is quite difficult to develop and massively produce such products. The other commonly used method in the conventional technique is adding the polymer into the liquid crystal layer. In such case, when the liquid crystal molecules are in the bend state, the ultraviolet (UV) is emitted onto the polymer to form a polymer wall, such that the liquid crystal molecules are sustained to be arranged with the bend state. Although such method is quite simple, a light leakage phenomenon will occur in the OCB LCD. In addition, other methods are available, for example, forming slits on the pixel electrode or forming protrusions above the pixel structure by applying a special pixel design, such that the arrangement of the liquid crystal molecules in some areas is changed, and the speed of transiting from the splay state to the bend state is improved.